What do you do when you've undertaken the diagnosis steps written about in my article titled " Compressed air leaking? Is it the valve or is it the cylinder?" in this E-zine, and you have determined that it is the air cylinder that is the problem?

The seals inside the air cylinder that allow the cylinder to function and those that keep the air inside the cylinder where it is supposed to be wear out over time through normal cylinder use.

When they do, your air cylinder could leak air to atmosphere past the rod seals. It might be losing compressed air faster through rod seal leaks than it can flow into the cylinder port from the air line. The cylinder won't produce the force you need for your application if that is the case, or, may not do the work required due to air blowing by the piston seals internally.

If the air cylinder is a non-repairable type, recognizable by the cylinder barrel being "rolled" into a groove on the end caps, then you cannot take this type apart, and it is time to discard it and buy a new one.

If your application is high cycle, and the cylinder is 1 1/2" bore and larger, it might be a cost effective idea to replace the "throw-away" cylinder with a repairable type. A repairable cylinder will be higher priced up front, yet the savings could be realized through a much longer service life with, as necessary, simple seal changes to keep the cylinder operating at peak performance.

Let us assume that your cylinder is repairable, perhaps an NFPA type, and it isn't working.

Rather than first taking the cylinder to a shop to determine the problem, take it apart in your shop. Usually all this will entail is to remove the nuts or bolts on the end of the tie rods on the rod-end of the cylinder, and pull that cap off.

The cylinder rod will be extending through the rod-end cap, so as you remove that cap, you will get the rod, piston and end cap as a unit.

Examine the cylinder rod. Is it scored or scratched? If so, then these imperfections will likely be cutting the seals where the rod passes through the rod-end cap. If it is those seals that are leaking now, replacing them will only solve the problem for a short time before they start to leak again.

Why is the rod scored? Has external debris being carried back to the rod wiper and lodged there? That may be what is scratching the rod. If there is no debris, check that the seals inside the rod bearing are not worn to the point where there's metal to metal contact abrading the surface of the rod?

If the rod is scored, replace it. Most piston rods are threaded and screw into the piston, with some sort of sealing compound to prevent the rod from vibrating loose. Examine where the rod meets the piston to be sure that it has not been tack welded. Weigh the cost of a new rod against the cost of replacing the whole cylinder to see which course of action is the right one for you.